The overall objective is to apply quantitative histochemical techniques to problems of renal physiology and biochemistry. The purpose is to circumvent the heterogeneity of the kidney by direct analyses of the different segments of individual nephrons. (a) One specific objective is to contribute to the understanding of the locations and mechanisms of renal transport processes by examining the chemical changes along the nephron during active transport. What is proposed is a new approach to the study of renal transport processes. Identified portions of individual nephrons from kidneys engaged in active transport will be directly analyzed for (1) the transported substance, (2) a marker of glomerular filtrate such as inulin, and (3) substances that might be involved in the transport process, e.g. high energy phosphates, metabolic derivatives of the substance transported. It is believed that the new approach will complement older methods of study of kidney function. (b) A second objective is to pinpoint the location and clarify the mechanisms of other renal functions such as gluconeogenesis and ammoniagenesis.